<section>
  <h3>Unless</h3>
  <button class="btn btn-primary" (click)="showUnless = !showUnless">toggle unless {{ showUnless }}</button>
  <p *appUnless="showUnless">测试 unless directive -- {{ showUnless }}</p>
  <p *appUnless="showUnless as un">测试 unless directive-- {{ un }}</p>
  <p *appUnless="showUnless; let un; let attr=attr;">测试 unless directive -- {{ un }}--attr: {{ attr }}</p>
</section>